Calculate Position Size with Commission Include in Formula

Determining the correct position size in trading is crucial for managing risk and maximizing returns. When commissions are involved, the calculation becomes more complex. This guide explains how to calculate position size while accounting for commissions, provides a step-by-step formula, and includes an interactive calculator to simplify the process.

How to Calculate Position Size with Commission

Calculating position size with commission involves several key factors:

Account balance - The total amount of money available for trading
Risk tolerance - The percentage of your account you're willing to risk per trade
Stop-loss distance - The price difference between entry and exit points
Commission per trade - The fee charged by your broker for each transaction

The basic approach is to determine how much you can afford to lose per trade based on your risk tolerance, then adjust for the commission costs. This ensures you're not overleveraging your account while accounting for the fees that will be deducted from your profits.

Important Note: Always use a stop-loss order to limit potential losses. The calculations here provide a starting point, but actual trading involves market conditions and other factors.

The Formula

The position size calculation with commission can be expressed as:

Position Size = (Account Balance × Risk Tolerance) / (Stop-Loss Distance + Commission)

Where:

Account Balance - Your total trading capital
Risk Tolerance - The percentage of your account you're willing to risk (e.g., 1% = 0.01)
Stop-Loss Distance - The price difference between entry and stop-loss points
Commission - The total commission per trade (both entry and exit)

This formula ensures you're accounting for the commission costs in your position sizing, preventing you from overtrading due to fees eating into your potential profits.

Worked Example

Let's calculate a position size with commission using these values:

Account Balance: $10,000
Risk Tolerance: 2% (0.02)
Stop-Loss Distance: $50
Commission per trade: $10 (both entry and exit)

Position Size = ($10,000 × 0.02) / ($50 + $10) = $200 / $60 ≈ 3.33 shares

This means you should only trade approximately 3.33 shares of this stock to maintain your 2% risk tolerance while accounting for the $10 commission per trade.

Factor	Value
Account Balance	$10,000
Risk Tolerance	2% (0.02)
Stop-Loss Distance	$50
Commission	$10
Position Size	3.33 shares

Interpreting the Results

The position size calculation helps you determine:

How many shares you can safely trade without risking too much capital
Whether the trade is worth pursuing given your risk tolerance and commission costs
How to adjust your position size if market conditions change

Remember that this is a simplified calculation. Actual trading involves:

Market volatility and unexpected price movements
Liquidity of the stock or asset
Broker-specific commission structures
Tax implications

Pro Tip: Always review your position size before entering a trade, especially when commissions are involved. The market can move quickly, and your initial calculations may need adjustment.

Frequently Asked Questions

Why is commission important in position sizing?: Commission affects your potential profit and risk per trade. Ignoring it can lead to overtrading or unrealistic position sizes that don't account for actual costs.
How do I find my broker's commission rates?: Check your broker's fee schedule or contact customer support. Commission rates vary by asset type, account type, and trading volume.
Can I use this formula for all types of trading?: This formula works for most equity and forex trading. For options, futures, or other complex instruments, you may need additional factors in your calculation.
What if I don't know the stop-loss distance in advance?: Use historical volatility or technical analysis to estimate a reasonable stop-loss distance. You can always adjust your position size after the trade is set up.
How often should I review my position size calculations?: Review your position size before each trade, especially when market conditions change. Commission rates may also vary based on your trading volume.